Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (TB) and leprosy (Ryan & Ray (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill.; herein incorporated by reference in its entirety). Mycobacteria can colonize their hosts without the hosts showing any adverse signs. For example, billions of people around the world have asymptomatic infections of M. tuberculosis. Mycobacteria are naturally resistant to a number of antibiotics, such as penicillin, and many other antibiotic-resistant strains have emerged.
Mycobacteria are classified as M. tuberculosis complex (MTBC) or non-tuberculosis mycobacteria (NTM) for the purposes of diagnosis and treatment. MTBC comprises species which can cause tuberculosis: M. tuberculosis, M. bovis, M. africanum, M. canetti, and M. microti. NTM are all the other mycobacteria, which can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, disseminated disease, Hansen's disease, and leprosy. Of the MTBC and NTM, different species are more or less common in different regions of the world, and exhibit different pathogenic and virulence characteristics.
The presence of antibiotic resistant TB, and multidrug-resistant TB (MDR TB) and extensively drug resistant TB (XDR TB) in particular, is of great concern to the medical community. MDR TB is TB that is resistant to two first-line anti-TB drugs, isoniazid and rifampicin, which are typically are used to treat all persons with TB disease. XDR TB is currently a relatively rare type of MDR TB, defined as TB that is resistant to isoniazid and rifampin, plus resistant to any fluoroquinolone and at least one of three injectable second-line drugs (e.g., amikacin, kanamycin, or capreomycin). Because XDR TB is resistant to first-line and second-line drugs, patients are left with treatment options that are much less effective. Resistant forms of TB raise concerns of a future TB epidemic with restricted treatment options, and jeopardize the progress made in worldwide TB treatment and control.
Mycobacteria infection can commonly consist of a mixed infection of: mycobacteria in the presence of other infectious agents, NTM and MTBC, different species of NTM or MTBC, and/or mycobacteria with different antibiotic resistance profiles.